This should tell you what your threads were doing when Thread Stack Dump was taken.

You may want to take Thread Stack Dump multiple times to look for potential problems.

If a very large number of Threads are in BLOCKED state, it is a sure sign of problem, the stack trace tells you what the Thread is blocked on. For example if there is a problem with Logging, it is seen that over a period of time All Threads get Blocked on Logging activity, and in therefore stalling the application.